1. Field of the Invention
The present invention relates to an optical magnetic disk recording/reproducing apparatus for high density digital recording, and the playback signal processing circuit thereof.
2. Description of the Prior Art
Optical magnetic disk recording/reproducing devices have been developed and marketed by numerous companies in recent years as high capacity data storage devices with a high data transfer rate. Commonly known as magneto-optical disk drives, read/write magneto-optical drives are still technologically immature in many ways, and particular improvement in the stability of the data reading, writing, and erasing operations is needed.
The present invention therefore relates to an optical magnetic disk recording/reproducing apparatus comprising a reproducing component that reproduces a stable address signal for the data recording and erasing operations.
The conventional optical magnetic disk recording/reproducing apparatus is described below with reference to the accompanying FIGS.
FIG. 1 is a block diagram of the reproducing device in a conventional optical magnetic disk recording/reproducing apparatus. In this device a magneto-optical disk 1 is driven by a spindle motor 2, and data is recorded to and reproduced from the magneto-optical disk 1 by the optical head 3. The optical head 3 in turn comprises a laser, lens, actuator, and polarized beam splitter. The laser power of the optical head 3 is controlled according to the control signal 24 output by the laser drive circuit 4. The magnetic bias 5 is used to modify the magnetic properties of the magneto-optical disk 1. The outputs from the photoelectric voltage conversion circuits 6-9 are added by adding amplifier circuits 10 and 11, the outputs of which are input to adding amplifier circuit 12 and differential amplifier circuit 13. The selector switch circuit 15 is controlled by control signal 18 to choose either the adding amplifier 12 or differential amplifier 13 output. The output from the selector switch circuit 15 is applied to the automatic gain control circuit 19 and digitizing circuit 16, and further to the detection circuit.
The address area, which is output from the adding amplifier 12, and the data area, which is the output from the differential amplifier circuit 13, are selected by the selector switch circuit 15 to generate and output a single signal consisting of both an address and a data area. The signal from the selector switch circuit 15 is applied to the automatic gain control circuit 19 for gain control.
The AGC 19 controls the gain of the output signal from the selector switch circuit 15, as shown in FIG. 2. During data reproducing mode, since the address signal and data signal waveforms have nearly equal amplitude, the output of the AGC 19 does not result in any gain change in the address area and data area. However, during writing or erasing mode, the amplitude of the data signal is amplified by a predetermined amount (FIG. 2 waveform (a)) to increase the laser power incident to the magneto-optical disk 1. Thus, the address signal level deforms during these modes in response to the change in the data signal. Furthermore, signal saturation in the data area also occurs. To remove such a drawback the automatic gain control circuit 19 is provided so that the data area gain is reduced as shown in FIG. 2 waveform (b). The output signal is then converted to a digital signal by the digitizing circuit 16, and then output to the detection circuit.
The problem with this construction, therefore, is that need for an automatic gain control circuit 19 to enable stable reproduction of the address area and data area during data recording, erasing, and reproduction results in an unavoidable increase in device size.
In addition, since the response of the automatic gain control 19 is very slow, it is difficult to enable stable detection of the address area, such as the sector mark, during data recording and erasing because of the residual level changes in the address area.